border-1px($color)
    position:relative
    &:after
        display:block
        position:absolute
        left:0
        width:100%
        bottom:0
        border-top:1px solid $color
        content:' '
border-none()
    &:after
        display:none
bg-image($url)
    background-image :url($url+'@2x.png')
    @media (-webkit-min-device-pixel-ratio:3),(min-device-pixel-ratio:3)
      background-image :url($url+'@3x.png')
